The long term goal of the proposed research is to determine how each of the major salivary glands comes to express a unique repertoire of secretory proteins. These studies will use the development of the rat submandibular gland as a model system. At birth, the gland contains two transient secretory cell types. Type III cells produce three dominant secretory proteins termed SMG-A, -B1 AND -B2, while type I cells synthesize a fourth abundant product, protein C. The synthesis of all four proteins is developmentally regulated. Between postnatal days 3 and 9, a third secretory cell type, the type IIIP cells, is transiently present in the developing submandibular gland. These cells, which are thought to be the immediate precursor to the adult acinar cells, synthesize all four predominant neonatal proteins as well as the adult submandibular gland acinar cell products GRP and mucin. As development continues, the type IIIp cells disappear and production of the neonatal proteins wanes. The gland is increasingly populated by early seromucous acinar cells, with a concomitant commitment to GRP and mucin biosynthesis. Thus, the period between postnatal days 3 and 9 appears to be a critical one for the regulation of gene expression by the submandibular gland. The specific aim of the proposed research is to characterize the neonatal proteins SMG-A, -B1, -B2 and C, and to compare the transcriptional control of their biosynthesis with that of the adult submandibular gland acinar cell-specific proteins GRP and Spt-1. A cDNA library will be prepared from 5 day old rat submandibular gland RNA, and clones encoding SMG-A, -B1, -B2 and protein C identified and sequenced. The initiation and accumulation of transcripts encoding these proteins will be observed throughout development using a combination of northern blot, dot blot, nuclear runoff and in situ hybridization analyses. These studies will demonstrate the roles played by transcriptional and post-transcriptional gland seromucous acinar cell phenotype. In future years, the information and materials obtained in this study will be the basis for the identification and characterization of regulatory elements controlling the expression of the diverse array of secretory proteins produced by the major salivary glands.